The present invention relates to a photosensitive member containing a low molecular weight organic compound.
A generally known direct method of electrophotography comprises; formation of an electrostatic latent image on the surface of the photosensitive layer of a photosensitive member by electrification and exposure; making said image visible by development with a developer; formation of copied images from said visible image directly from the photosensitive member, or by a toner image transfer method, which comprises transferring the visible image on the photosensitive member onto a transfer paper such as that of an ordinary paper and the copy by fixing the transferred image, or by a latent image transfer method which comprises transferring an electrostatic latent image from a photosensitive member onto a transfer paper and developing and fixing said electrostatic latent image on said transfer paper.
The photoconductive material forming the photosensitive layer of a photosensitive member in the area of electrophotography dealt with herein, conventionally use inorganic photoconductive material such as selenium, cadmium sulfide or zinc oxide. Such photoconductive materials have advantages in that they may be charged to an appropriate potential in the dark, the loss of electrical charge in the dark is limited, the electric charge can be dissipated fast with irradiation of light, and so on. However, they do have disadvantages. For example, a selenium photosensitive member has a high production cost, and its inadequate resistivity to heat and mechanical impact necessitates caution in handling. Photosensitive members based on cadmium sulfide or zinc oxide do not have stable sensitivity in a highly humid environments and, moreover, colorant added as a sensitizer undergoes electrification deterioration due to corona charge and color fading due to exposure to light, they are lacking in stability of properties in long periods of use.
Consideration has also been given to the use of various organic photoconductive polymers, including polyvinyl carbazole. Although such polymers have advantages over the above inorganic photoconductive materials in film forming properties, lightness in weight, etc., they are inferior to the inorganic products comprising sensitivity, durability and stability to change of environmental conditions.
An organic photoconductive compound of a low molecular weight also has an advantage in that the property of the film formed, and the electrophotographic property, can be controlled by using the right kind and the right composition ratio of binder used in combination. However, combination with a binder requires the organic compound to have high compatibility with binder.
A photosensitive member consisting of an organic photoconductive compound of high or low molecular weight dispersed in a resin binder has disadvantageously large residual potentials and low sensitivity, because of many traps for the carrier. To solve this problem it has been proposed to incorporate a charge transporting material into an organic photoconductive compound.
Many organic compounds have been named for use as charge transporting materials, but this practice brings many problems to the fore. For example, U.S. Pat. No. 3,189,447 described the use of 2,5-bis(P-diethylaminophenyl)-1,3,4,-oxadiazole, however its compatibility with binders is low and the material tends to separate into crystals. The U.S. Pat. No. 3,820,989 described the use of a diarylalkane derivative, which has satisfactory compatibility with binders but repeated use causes change in sensitivity. The hydrazone compound in the Japanese Patent KOKAI No. 59143/1979 is fairly satisfactory with respect to residual potential, but shows defects with respect to sensitivity, chargeability and the properties affected by repeated use.
It has thus been almost impracticable to introduce a low molecular weight organic compound as a component of a photosensitive member to bring about satisfactory effects.